What was the reason chickens shouldn't have uncooked beans?

Just wondering because mine found some dried pole bean pods in the garden yesterday and were extracting and eating the beans... I don't think they ate a whole lot of them because it takes some effort to beat the beans free but it was more than one or two each. They seem fine today

It had something to do with trypsin...something about inhibiting nutrient absorbtion...do a search on beans or soybeans. It's probably like choc. w/dogs....a little won't do much harm, but a lot would.

Raw or undercooked dried bean poisoning is very real, but very rare, because most people will not eat raw dried beans. Although undercooked beans seem to be worse than raw. I have no idea how it would effect chickens, although it would be prudent to avoid them.
Here some info:

Red Kidney Bean Poisoning is an illness caused by a toxic agent, Phytohaemagglutnin (Kidney Bean Lectin). This toxic agent is found in many species of beans, but it is in highest concentration in red kidney beans (Phaseolus vulgaris). The unit of toxin measure is the hemagglutinating unit (hau). Raw kidney beans contain from 20,000 to 70,000 hau, while fully cooked beans contain from 200 to 400 hau. White kidney beans, another variety of Phaseolus vulgaris, contain about one-third the amount of toxin as the red variety; broad beans (Vicia faba) contain 5 to 10% the amount that red kidney beans contain.

As few as 4 or 5 beans can bring on symptoms. Onset of symptoms varies from between 1 to 3 hours. Onset is usually marked by extreme nausea, followed by vomiting, which may be very severe. Diarrhea develops somewhat later (from one to a few hours), and some persons report abdominal pain. Some persons have been hospitalized, but recovery is usually rapid (3 - 4 h after onset of symptoms) and spontaneous.

The syndrome is usually caused by the ingestion of raw, soaked kidney beans, either alone or in salads or casseroles. As few as four or five raw beans can trigger symptoms. Several outbreaks have been associated with "slow cookers" or crock pots, or in casseroles which had not reached a high enough internal temperature to destroy the glycoprotein lectin. It has been shown that heating to 80 degrees C. may potentiate the toxicity five-fold, so that these beans are more toxic than if eaten raw. In studies of casseroles cooked in slow cookers, internal temperatures often did not exceed 75 degrees C..

All persons, regardless of age or gender, appear to be equally susceptible; the severity is related only to the dose ingested.

No major outbreaks have occurred in the U.S. Outbreaks in the U.K. are far more common, and may be attributed to greater use of dried kidney beans in the U.K., or better physician awareness and reporting.

NOTE: The following procedure has been recommended by the PHLS (Public Health Laboratory Services, Colindale, U.K.) to render kidney, and other, beans safe for consumption:
* Soak in water for at least 5 hours.
* Pour away the water.
* Boil briskly in fresh water for at least 10 minutes.
* Undercooked beans may be more toxic than raw beans.

Mouldy grain, now that can be catastrophic. But a few peas or beans snatched from a garden bed? I doubt there'll be an issue.

I've seen liver damage from uncooked sweet lupins, which are a type of bean. However I was feeding these regularly at 10% of the diet. Incidentally the damage I saw was much milder than liver damage from commercial meat grower, which appeared to turn the livers into orange mush in a period of weeks.

Realistically, a great many (perhaps even all) feedstuffs have certain levels above which it could be said they're 'toxic'. The trick is balance, and generally speaking chickens are quite good at managing it.

I've noticed my chickens don't generally try to eat things that are poisonous to them. Usually plants that are very poisonous have some sort of strong or unpleasant taste, since it's in the plants interest to discourage animals from eating it anyway, rather than to kill the animal AFTER the plant has been eaten. Lower level toxins are another matter, but depending on who you ask, lots of things have low-level toxicity or antinutrients--including common food ingredients, so I think it's important not to get carried away, just because someone, somewhere, says that something is "toxic"... The OP was about dried pole beans--I don't think there's any issue with the chickens eating a few of those. Personally, my chickens (and the wild chickens) love eating Pidgeon Peas (I type of perennial pulse) and will shell them out of the pods themselves or eat the ones that have shattered off the bush... I also feed them cowpeas that have bean weevils in them, or the seeds of snap beans that have gotten too tough to eat.

Junk food is toxic, for that matter (it causes all kinds of health problems), but look how many people eat that...